Several unidentified flying objects have been spotted in the United States, leading some to ask if they are aliens or something more sinister. Euronews asked the experts to find out.
It's the stratospheric saga that's gripping the world. Almost two weeks ago, the US accused China of sending a spy balloon high above its territory - grabbing the attention of sci-fi geeks and Pentagon officials alike.
Beijing officials admitted the object did belong to them but claimed it was a meteorological research aircraft that had blown off course, and said that US balloons have entered Chinese airspace more than a dozen times in the past year.
The US State Department said that before the object was shot down, it was analysed mid-flight by U-2 planes, which allegedly photographed surveillance equipment such as antennas, and thus revealing its true mission.
In the three days that followed, three more unidentified flying objects were destroyed over North America.
US officials have said that the objects have not been threatening - causing conspiracy theories to develop, some concerning UFOs.
The White House has dismissed this and spokeswoman Karine Jean-Pierre cracked a smile in the press room when she said, "I loved ET, the movie, but we're gonna leave it there."
A question of height?
Very few facts have been confirmed. But one thing we do know is that the alleged spy balloon was flying at an altitude of 18 kilometres, in the middle of the stratosphere.
For Jean-Vincent Brisset, an expert at the Institute of International and Strategic Relations (IRIS), this may be easily explained.
"Currently, the United States, but also China, France, no doubt Russia, and other major countries, are conducting research to try to develop new weapons, so-called hypersonic gliders."
"A large part of the flight of these devices takes place in the stratosphere. We know very little about the stratosphere, in terms of composition, in terms of the winds that circulate," Brisset added.
So is the Chinese balloon an exploratory device with the mission of discovering a strategic stratosphere where any weapon of war will be very difficult to intercept?
"This region of the atmosphere is above the belt where planes fly and below the space. It's a region we don't fully know". And, therefore, an advantage for whoever can do it," Iain Boyd, Director of the Center for National Security Initiatives at the University of Colorado told Euronews.
Procedures have changed and so have the objects
The North American Aerospace Defense Command (NORAD) tightened the precision of the radar system after the first balloon was spotted, which may explain the increase in the detection of devices thereafter.
The debris from the "spy balloon" could have reached populated territory, hence why it was only shot down over the Atlantic.
Iain Boyd told Euronews that he thinks the aircraft was too big to be a meteorological device, but he also doubts that Beijing would send compromising material that is so easily detectable and could fall into American hands.
On the same day, Bogotá confirmed that another similar object flew over Colombia. No action was taken to destroy it.
The latest device to be intercepted was identified in Michigan. It was 6 kilometres high and posed a significant danger to civil aviation.
Jean-Vincent Brisset said remains unsure as to why there are no photographic records of the object or the planes that shot it down, but acknowledged that countless devices are launched every day, and although most have locators, the trajectory can be unpredictable, and depend on factors such as the wind.